1. Field of the Invention
The invention relates to apparatus for drying rigid or semi-rigid sheet material having one or a plurality of tiered horizontal conveyors and utilizing force circulated, horizontal flow, gases in contact with the material to be dried for drying the same.
2. Description of the Prior Art
Single and multiple deck roller dryers for reducing the moisture content of rigid and semi-rigid material in sheet form, such as, green veneer, wet plasterboard, fiberboard, Masonite mat, and the like, wherein the material being dried is conveyed through a stationary housing on one or a plurality of tiered single or double roll conveyors while heated gases are circulated through the housing or a part thereof are known. Such devices have many disdvantages one of which is loss of efficiency because of the entrance of air at ambient temperature into the dryer through the material discharge opening or openings in the dryer.
Roll conveyors are typically employed in dryers of the type with which the present invention is particularly concerned. Single roll conveyors are usually employed in so-called "board" dryers used in the manufacture of such products as fiberboard, plasterboard, and the like, and double or pinch roll conveyors are typically employed in so-called "veneer" dryers because veneer tends to warp upon drying. In either single or double roll dryers the material is typically discharged through pinch rolls at the material discharge end thus making it easier to seal the material discharge end of the dryer then when a single roll is employed. The loss of efficiency in dryers employing pinch rolls at the discharge end is nevertheless substantial. A typical pinch roll type dryer is disclosed in U.S. patent to Morris U.S. Pat. No. 3,299,533.